When manufacturing plastics products in the form of tubes certain problems are encountered concerning the strength of the material. One difficulty is to maintain an even temperature in the plastics substance. Even small differences in the temperature result in changes in the flowability. A locally increased temperature brings about a more rapid flow which means that a relatively bigger volume of material will pass out through the adjacent portion of the nozzle.
Furthermore deposits will often form in the nozzle, which will cause lines in the extruded products, so called dieliners. The risk of such die-liners is reduced, while simultaneously the temperature distribution in the substance will be uniform, if the substance is thoroughly worked just before the clearance of the nozzle.
The elongate molecular chains in the substance will, during the extrusion through the clearance, be oriented in the direction of flow, which, together with the tendencies to local temperature variations and possible dieliners, may result in weak spots in the ready products, which are especially marked if a tubular preform is expanded to foil thickness.
The aim of the present invention is to propose a method and an extruder nozzle for producing plastics products by extrusion of a plastics substance through a clearance opening between an inner component and an outer component.